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BIO230 > Cell communication > Flashcards

Cell communication Flashcards

1
Q

examples of unicellular communication

A

quorum sensing in bacteria
- release and response to chemical signals

mating in budding yeast
- signaling b/w yeast cells prepares them to mate

aggregation of ameboid cells
- signalling between dictyostelium cells draws them together

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2
Q

two main ways of receiving a signal

A
  1. cell-surface receptors
    - for hydrophilic signal molecules
  2. intracellular receptors
    - for hydrophobic molecules
    - has to pass through the membrane of the target cell
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3
Q

contact-dependent signaling

A

signals retained on the cell surface

- faster

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4
Q

pararcrine signaling

A
  • signals released from the cell but act locally

restricted by

  • internalization by neighbouring cells
  • signal instability or destruction by extracellular enzymes
  • binding to extracellular matrix molecules
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5
Q

synaptic signaling

A

neuron reaches a long distance then communicates

  • neurons extend acons to contact distant target cells
  • the released signaling molecules act locally at target
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6
Q

endocrine signaling

A

endocrine cells secrete hormones into the bloodstream for long-range distribution
- diffusion out of blood into target cell

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7
Q

signal transduction

A

the conversion of extracellular signals into intracellular signals

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8
Q

effector

A

downstream molecule in a signal transduction pathway

- upstream molecules have their effects on them

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9
Q

signal transduction pathway

A

extracellular signal molecule –> receptor protein –> intracellular signaling proteins –> effector proteins

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10
Q

effector proteins (3)

A
  • metabolic enzyme
  • gene regulatory protein
  • cytoskeletal protein
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11
Q

second messengers

A

small intracellular signaling molecules

  • made in large numbers and diffuse through cytoplasm or plasma membrane
  • bind and alter effector molecules
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12
Q

signaling by phsophorylation

A

for serine/threonine kinases and tyrosine kinases

  • phosphorylation, powered by ATP hydrolysis turns ON
  • dephosphorylation turns OFF
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13
Q

signaling by GTP binidng

A
  • large trimeric and small monomeric type proteins
  • have low GTPase activity
  • GTP binding (GDP –> GTP) turns ON
  • GTP hydrolysis (regulated by GAP) turns OFF
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14
Q

GAPs

A

GTPase activating proteins

- increase the GTP hydrolysis

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15
Q

GEFs

A

Guanine nucleotide exchange factors

- promote the exchange of GDP for GTP

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16
Q

examples of signaling pathways

A
  • SH2 and PTB domains bind phosphotyrosine containing sequences
  • PH domains bind phosphoinositides
  • SH3 domains bind proline-rich sequences
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17
Q

synaptic signaling specificity

A

neurons make connections with specific target cells

  • all based on location
  • the same neurotransmitter can be used
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18
Q

endocrine signaling specificity

A

different molecules are released and target cells express specific receptors to respond to specific molecules

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19
Q

what prevents an upstream signal from activating all of the pathways?

A

the formation of local complexes helps insulate pathways from each other
- must be activated by an activated receptor

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20
Q

coincidence detectors

A

only activate downstream signals when two upstream signals are both detected

  • pathway is activated
  • protein kinase phosphorylates y, each specific to one side of y
  • downstream signals are only activated if y is phosphorylated on both sides
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21
Q

what determines the response speed to a signal

A

it varies depending on the cellular machinery involved

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22
Q

effects of positive feedback

A
  • enhancing the response
  • strong enough feedback can be self-sustaining
  • bistable systems can stably exist in on or off states
23
Q

effects of negative feedback

A
  • if it occurs quickly, signal is suppressed
  • allows cells to respond to changes in upstream signals and a wider range of signal strengths
  • if it occurs slowly, the system can oscillate
24
Q

NO as a signaling molecule

A
  • made by deamination of arginine by NO synthases
  • acts locally
  • affects smooth muscle and other target cells
  • rapid diffusion of NO can cause relaxation of smooth muscle cells
25
Q

steroid hormones

A
  • made from cholesterol

- affect sexual characteristics and metabolism

26
Q

thyroid hormones

A
  • made from tyrosine

- increase metabolic rate

27
Q

retinoids

A
  • made from vitamin A

- regulate development

28
Q

vitamin D

A

affects metabolism

29
Q

nuclear receptor superfamily

A
  • contain binding sites for a small hydrophobic molecule as well as for DNA
  • 48 in the human genome
  • more than half only identified based on sequence analysis
30
Q

ligand binding and conformation

A
  • binding to a ligand induces conformation and release of inhibitors
  • DNA binding and downstream transcription promoted
31
Q

ion channel properties

A
  • narrow selective pores
  • open and close rapidly
  • transport is passive (based on electrochemical gradients and ion diffusion)
32
Q

different types of ion channels

A
  • voltage gated
  • ligand gated (intracellular and extracellular)
  • mechanically gated
33
Q

ion channel functions

A
  • electrical excitability of muscle cells
  • electrical signaling in the nervous system
  • leaf closure responses in plants
  • signal the single-celled paramecium to reverse its movement upon collision
34
Q

nerve impulses

A
  • synaptic vesicles release neurotransmitters through exocytosis
  • these bind to and open ligand gated channels
  • channels allow ion passage into the target cell to create another nerve impulse or a different effect
35
Q

GPCR

A

G-protein coupled receptors

  • 7 pass transmembrane proteins
  • activated by proteins, small molecules, and light
  • more than 700 in humans
36
Q

GPCR signaling

A
  • signaling done via a membrane associated trimeric GTP-binding protein
  • functions as a GEF to change GDP –> GTP on the alpha subunit
  • a subunit goes through a conformational change and induces release of other subunits
  • subunits bind to downstream effectors
  • turned off by a regulator of G protein signaling (RGS) which acts as a GAP
37
Q

cAMP and its pathway

A
  • synthesized from ATP by adenylyl cyclase
  • destroyed by cAMP phosphodiesterase
  • signal is transduced by increasing adenylyl cyclase activity above a constant background of phosphodiesterase activity
  • cAMP activates PKA which phosphorylates CREB to activate transcription
  • release of separate molecules forms a tetramer
38
Q

GPCR signaling via calcium

A
  • signal molecule activates GPCR
  • Gq is acivated by GTP
  • activated phospholipase C-b causes release of IP3
  • diacylglycerol is left behind on the membrane
  • IP3 diffuses through cytoplasm amd activate IP3 gates
  • Ca2+ released and activate PKC
39
Q

enzyme-coupled receptors

A
  • receptor tyrosine kinases
  • receptor serine/threonine kinases
  • histidine-kinase-associated receptors
40
Q

signaling by receptor tyrosine kinase

A
  • ligand binding dimerizes the receptor
  • kinase domains brought together and phosphorylate each other at the same time
  • phosphorylation of kinase domains enhances activity
  • phosphorylation of other regions creates docking sites to assemble a signaling complex
  • recruition of proteins that mediate downstream signaling
41
Q

what happens when a defective kinase domain is expressed with a normal receptor?

A

the cell has reduced response to the signal

42
Q

drosophila and tyrosine kinase

A
  • omnatidia compose of photoreceptor and support cells
  • arise from epithelial sheet through sequential differentiation of the photoreceptor cells
  • R7 is last to differentiate and needed to detect uV light
43
Q

Sevenless mutant

A
  • helped discover what was necessary for R7 differentiation

- normal Sev protein shown to be a receptor tyrosine kinase in R7 cells

44
Q

Bride-of-sevenless (Boss)

A

ligand for Sev expressed on R8 cells

45
Q

Drk and Son-of-Sevenless (Sos)

A
  • Drk links Sev to Sos

- Sos is a GEF for Ras

46
Q

Ras

A

a molecular switch downstream of receptor tyrosine kinase

  • monomeric GTPase
  • attached to cytoplasmic face of the plasma membrane by a lipid anchor
  • activated by Ras-GEF and inactivated by Ras-GAP
  • leads to cell proliferation
47
Q

Ras and MAP kinase module

A
  • Ras activated MAPKKK
  • phosphorylates MAPKK
  • phosphorylates MAPK
  • phosphorylates effecor proteins
  • changes in protein activity and gene expression
48
Q

receptor serine/threonine kinases

A
  • largest class, 6 major families in plants
  • Clv1/Clv2 signals stimulate the development of stems, leaves, and flowers
  • ser-thr kinase phosphorylates itself and its neighbour
  • protein phosphatase can turn off the signal through dephosphorylation
49
Q

histidine-kinase-associated receptors

A
  • activate a two component signaling pathway
  • used by bacteria, yeast, and plants
  • repellent binds to receptor activating CheW
  • CheA is activated, phosphorylates itself and transfers the phosphate onto CheY
50
Q

lateral inhibition by notch signaling

A
  • top cell inhibits notch activation
  • both start off with delta and prevent each other’s delta expression
  • each cell inhibits its neighbour
  • cell with active delta specializes
51
Q

activating a notch cell

A
  • delta binds to big fragment
  • top cell has to endocytose the large one
  • mediated by clathrin
  • rest of notch is activated down
52
Q

notch cell pathway

A
  • cleavage at site 1
  • transport to plasma membrane
  • binding to delta, endocytosis of delta-notch-fragment complex and cleavage at site 2
  • cleavage at site 3
  • notch tail migrates to nucleus
  • protein complex containing notch tail activates gene transcription
  • leads to inhibition of delta expression and cell specialization
53
Q

Sonic hedgehog

A
  • source of morphogen
  • Shh spreads and the gradient controls formation of distinct digits
  • without it, CI is sequestered in the cytoplasm by a microtubule associated complex
  • promotes proteolysis of Ci to a transcriptional repressor
54
Q

Patched

A

binding with Hedgehog allows smoothened to transfer to the plasma membrane and release Ci from its inhibitory complex
- difference determined by presence or absence of a cut

BIO230 (4 decks)

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